Actually the last two posters both have the term "trail" mixed up.
Trail is the distance down on the ground between the center of the tire contact patch and the spot where the steering axis intercepts the ground. You control this with the angle of the frame's steer tube and the offset amount of the fork.
In the motorcycle world that angle is the rake angle and the offset is the offset. I'm coming to find that in the bicycle world this is altered and these are known as the steering angle and the rake or offset of the fork.
So a fork that has less rake or offset will result in the contact patch being further behind the steering axis to ground intersection point. That distance is the trail. So less rake = more trail.